Add audit tool to extract inconsistencies between users and buckets

[shino]

There is possibility of inconsistencies between the user bucket moss.users
and the buckets bucket moss.buckets because no transaction is (can be) used.

This PR adds tool for detecting inconsistencies between them.
Three kinds of inconsistencies:

1. Bucket object in buckets bucket is not tracked by the user
   in its value. ({not_tracked, {User, Bucket}})
2. A certain user thinks it owns a bucket but no objects in buckets bucket
   exists. ({no_bucket_object, {User, Bucket}})
3. A certain user thinks it owns a bucket but the bucket is actually
   owned by different user. ({different_user, {User, Bucket, DifferentUser}})

---

Sample execution by console command and log output in it:

% dev/dev1/bin/riak-cs-admin audit-bucket-ownership
[{no_bucket_object,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"corrupt">>}},
 {different_user,{<<"N4ADKYOVGZLKL5RVD0MA">>,<<"bob2">>,
                  <<"T_RNSHIN22TIJ1MKF8BP">>}},
 {not_tracked,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"missing-in-list">>}},
 {not_tracked,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"bob2">>}},
 {not_tracked,{<<"N4ADKYOVGZLKL5RVD0MA">>,<<"missing-in-bobs-list">>}}]

16:54:20.475 [info] Bucket is not tracked by user: {User, Bucket} = {N4ADKYOVGZLKL5RVD0MA, missing-in-bobs-list}
16:54:20.475 [info] Bucket is not tracked by user: {User, Bucket} = {T_RNSHIN22TIJ1MKF8BP, bob2}
16:54:20.475 [info] Bucket is not tracked by user: {User, Bucket} = {T_RNSHIN22TIJ1MKF8BP, missing-in-list}
16:54:20.475 [info] Bucket is owned by different user: {User, Bucket, DifferentUser} = {N4ADKYOVGZLKL5RVD0MA, bob2, T_RNSHIN22TIJ1MKF8BP}
16:54:20.475 [info] Bucket does not exist: {User, Bucket} = {T_RNSHIN22TIJ1MKF8BP, corrupt}

---

This PR is in the state of request-for-comment. Any comments on categorization,
log format, command line output, implementation, etc is appreciated.

[kuenishi]

Note: this work is for #1161 (RCS-211) .

[kuenishi]

~n would make this look better. Also, a message like "No inconsistency found." will be more informative when Inconsistencies is just [].

[kuenishi]

It worked;

$ curl -XPUT  'http://localhost:8098/buckets/moss.buckets/keys/test' -H "X-Riak-Vclock: a85hYGBgzGDKBVI8ypz/fp7QY+KCCCUy5rEyKCjLnOfLAgA=" -d "sub-key"
$ rel/riak-cs/bin/riak-cs-admin audit-bucket-ownership
[{different_user,{<<"admin-key">>,<<"test">>,<<"sub-key">>}},
 {not_tracked,{<<"sub-key">>,<<"test">>}}]

We would follow this with some pretty printing or documentation.

[kuenishi]

It would also be nice to output console.

[shino]

By discussion in chat, output to console may be very noisy when large number of inconsistencies.

[shino]

Thanks for review 😄 Updated.

[shino]

@borshop merge

[shino]

For release note: please look at the description at the top.

[shino]

micro benchmark with 100,000 users and 27,000 buckets and small inconsistencies:

% time ./dev/dev1/erts-5.10.3/bin/nodetool -name 'rcs-dev1@127.0.0.1' -setcookie riak rpc_infinity riak_cs_console audit_bucket_ownership
[{no_bucket_object,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"corrupt">>}},
 {different_user,{<<"N4ADKYOVGZLKL5RVD0MA">>,<<"bob2">>,
                  <<"T_RNSHIN22TIJ1MKF8BP">>}},
 {not_tracked,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"missing-in-list">>}},
 {not_tracked,{<<"T_RNSHIN22TIJ1MKF8BP">>,<<"bob2">>}},
 {not_tracked,{<<"N4ADKYOVGZLKL5RVD0MA">>,<<"missing-in-bobs-list">>}}].
./dev/dev1/erts-5.10.3/bin/nodetool -name 'rcs-dev1@127.0.0.1' -setcookie ria  0.28s user 0.11s system 0% cpu 2:18.44 total

[shino]

In local environment (single node cluster with ring size 8, not good for benchmark), it took a few seconds for list keys, it seems that getting every object in serialized way is current bottleneck. But, one more point, Riak CS node consumes CPU ~ 300%. Feels strange. Further investigation / optimization may follow in another ticket / issue.